A number of medical procedures involve or can be supplemented with the placement of an endoluminal prostheses, commonly referred to as a stent, that can be implanted in a lumen, such as a blood vessel or other natural pathway of a patient's body. Such stents typically define a generally tubular configuration, and are expandable from a relatively small diameter (low profile) to an enlarged diameter. While in its low profile configuration, the stent is advanced endoluminally, by a delivery device, through the body lumen to the site where the stent is to be placed. The stent then can be expanded to a larger diameter in which it can firmly engage the inner wall of the body lumen. The delivery device then is removed, leaving the implanted stent in place. In that manner, the stent may serve to maintain open a blood vessel or other natural duct, the functioning of which had become impaired as a result of a pathological or traumatic occurrence.
Among the medical procedures in which stents have had increasing use is in connection with percutaneous transluminal angioplasty (PTA), and particularly percutaneous transluminal coronary angioplasty (PTCA). PTA and PTCA involve the insertion and manipulation of a dilating catheter through the patient's arteries to place the dilatation balloon of the catheter within an obstructed portion (stenosis) of a blood vessel. The balloon then is expanded forcibly within the obstruction to dilate that portion of the blood vessel thereby to restore blood flow through the blood vessel. Among the more significant complications that may result from such angioplasty is that in a significant number of cases, the dilated site again becomes obstructed. By placing a stent within the blood vessel at the treated site, the tendency for such restenosis may be reduced.
Stenoses often may develop in the branching region of a patient's blood vessel. Treatment of a stenosis in the branched region may present numerous additional difficulties in the design of devices to dilate stenoses at the branched region. Techniques and devices have been developed to effect a dilatation at a branched region such as the "kissing balloon" technique described in U.S. Pat. No. 4,896,670. The need for an effective stent that can be placed at a bifurcated region has been recognized; although it is believed that no such effective device has previously been developed.
A number of stents have been proposed and developed in the art, including single stents that define a single luminal pathway as well as bifurcated stents that define a branched pathway and are intended to be placed in a branching region of a blood vessel. The development of bifurcated stents, as compared to single stents presents numerous difficulties because of the branched arrangement and the difficulty in delivering and placing a bifurcated stent at the branched region of a blood vessel.
U.S. Pat. No. 4,994,071 (MacGregor) discloses a design for a bifurcating stent intended to be inserted into a bifurcated blood vessel. The stent is constructed from two lengths of continuous wire, one of which is formed in a series of interconnected loops to define a common tubular branch and one of the bifurcated branches. The other length of wire also is formed in a series of similarly interconnected loops to define the other branch of the bifurcation. The two assemblies of interconnected loops are connected together to define a Y-shaped structure. The interconnection between the structure defining the bifurcated branches is said to enable them to be bent to conform to the shape of the vessels into which the device is intended to be inserted. The loops are formed so that they can be expanded from an initial diameter to facilitate insertion into the blood vessel to an expanded, deployed diameter.
The MacGregor device presents a number of difficulties. Its continuous wire construction does not readily lend itself to precise matching to the vascular anatomy of pathological situation of the specific patient in whom the stent is to be placed. The construction is adapted, as a practical matter, only to be manufactured in standard configurations and lengths. When a standard length of stent does not ideally match the patient's anatomy, the physician would be forced to choose among the available standard lengths and configurations in an effort to make a selection that, at best, could be considered to be a compromise. A further difficulty with the device described in the MacGregor patent is that it is intended to be placed in the patient while it is maintained in its preformed Y-shaped configuration. Although the device is intended to be advanced and placed at the target site with its circumferential loops in a radially contracted configuration (low profile), advancement and insertion in that configuration could be expected to significantly complicate the delivery and placement procedure. The device is described as being placed by advancing it through a guide catheter so that the loops of the bifurcating stent do not engage the inner walls of the blood vessel. Consequently, it may not be possible to place the device in a narrow blood vessel, such as a coronary artery, that is too small to accommodate a guide catheter in addition to the other components of the device. Still another difficulty presented by the device is that it cannot be expected to present a readily visualized image under fluoroscopy or X-ray during implementation as well as at a later time. The MacGregor stent being formed from a pair of single slender wires may be difficult, if not impossible, to visualize under fluoroscopy or X-ray.
It is among the general objects of the invention to provide an improved bifurcated endovascular stent that overcomes the above-disadvantages.